According the invention there is provided in one aspect a method, and in another aspect a system, for identifying in respect of a descending golf ball the position from among a plurality of launch positions from which the ball was launched, comprising a step of, or means for, measuring descent parameters of the descending ball to derive at least the time of descent of the descending ball and a measure dependent on its angle of descent in elevation, a step oft or means for, calculating an estimate of flight duration of the descending ball as a function of the measure of descent angle, a step of, or means for, measuring in respect of each launch position the interval of time between the launch of a ball from that position and the time of descent of the descending ball, a step of, or means for, comparing the interval of time measured in respect of each launch position with the calculated estimate of flight duration of the descending ball to determine for which of the launch positions the respective interval is a close match with the calculated estimate, and the step of, or means for, identifying the position from which the descending ball was launched with the launch position for which the close match exists.
A measure of the descent angle in elevation of the descending ball may be derived from measurements of component velocities of its descent trajectory.
References to ‘descent’ of a golf ball are intended to refer to the end portion of the carry trajectory of the ball as distinct from any part of its subsequent bounce or roll trajectory. Also, a ‘descending golf ball’ is intended to refer to a flying golf ball near the end of its carry trajectory and preferably within the last 10% of the trajectory. The end of the carry trajectory is the point where the ball hits a ‘target’ some distance from the initial launch position. The launch position may typically be, for example, one of several ‘tee-off bays’ of a driving range.
The present invention is applicable to all golf shots but is especially applicable to shots where the net aerodynamic force (i.e. the vector addition of lift and drag forces) is greater than 1.0 meters per second per second (m/s2) but more especially greater than 10 m/s2.
An aim of the present invention is to provide methods and systems of identifying golf shots that do not rely on flight prediction or trajectory tracking and do not require golf balls that are specially marked or electronically tagged or the like.
Flight prediction methods require expensive ball-launch measurement equipment capable of measuring the spin components of a ball and sometimes require special balls. Flight prediction is also subject to significant non-systematic errors caused by blustery wind and/or random variations in the aerodynamic properties of balls, which change due to surface degradation. Flight prediction methods can be enhanced by measurement of ball-landing positions and flight durations. However, systems that rely on measurement of only landing positions and times are inadequate since most of the information about a ball's flight history is destroyed on landing. Systems that identify individual golf shots using prediction of ball flight and measurement of landing positions are described in U.S. Pat. No. 6,179,720 and US-A-2007/0167247.
Trajectory tracking methods (such as video tracking or radar tracking systems) are very expensive, require large data processing means and may not work reliably when there are multiple concurrent balls in the flight space. Typically, one or more video cameras or radar tracking devices lock onto the flight path of one ball at a time and track that ball throughout its flight from initial impact to at least the final landing spot. This means that the cameras or radars must capture data almost continuously for several seconds whereas in the present invention measurements of the ball trajectory is only required for a few milliseconds just after initial impact and just prior to landing on the outfield. GB-A-2294403 describes a method of identifying golf shots by video tracking combined with swing measurements.
Identifying individual balls with tagging means such as embedded RFID chips is costly and the mechanical means of collecting balls to decode the RFID data is cumbersome and unreliable. Systems that identify individual golf shots using RFID tagging are described in JP-A-8224331 and also in U.S. Pat. No. 6,607,123.
Measurement of descent parameters, and of launch parameters, may utilise electro-mechanical, electro-acoustic, electro-magnetic, electro-optical, Doppler microwave radar, ultrasonic Doppler, high-speed video or any other technology that provides electronic measurement suitable for signal processing.
The measurement of the descent parameters may be made typically as the ball approaches a ‘target’ in the driving-range outfield. The target may be a marked-out circular, oval or rectangular area or the like or may be a landscaped golf green, mimicking a real golf course green. Various alternatively target designs may be used. For example, earthworks or structures resembling large archery targets, water features or large bunkers where balls land and disappear without bouncing out, and sundry other forms. Alternatively, the measurement may be made as the descending ball is about to land on any part of the entire outfield or a substantial part of it. Preferably, but without limitation, the descent parameters are measured within a short distance from the end of a ball's carry (e.g. in the final 5%, or more preferably the final 2% of the carry distance).
Limiting the extent of the measurement range of the descent reduces the cost of the measurement apparatus and improves measurement reliability. In a preferred embodiment, the descent parameters are measured within less than 2 meters of the landing surface or ground level and with apparatus that is itself less than 2 meters above ground level. Restricting the height of sensing apparatus in the outfield makes it much less obtrusive on the outfield landscape, which is highly desirable.
A preferred means for measuring the descent parameters at each target uses at least four ‘detection planes’. The said detection planes comprise fan beams with very small angular field of view normal to the detection plane and wide fields of view in the planes of the detection planes. Means are provided to sense the angular position (within the fan beam) and the instants of time when balls pass through the detection planes. Typically, the detection planes are arranged in two co-planar pairs that are parallel and offset, but pointing along different directions, so that the two-dimensional position of a ball as it passes through the common field-of-view plane can be found by triangulation. The time difference between the instants when the ball passes through the detection planes, and the offset separation distance between the planes containing the centres of the fields-of-view give a measurement of the ball's velocity vectors and its instantaneous position in space. Preferably, but without limitation, the fields of view of all the detection plane sensors are horizontal, or nearly so and positioned close to the surface of the outfield surface.
Measurements of parameters of launched balls are desirably made by means that is of low cost, and has reliability and wide ‘shot acceptance’. In this context, ‘shot acceptance’ means the ability of the measuring means to measure all types of shots as they leave the tee-off spot in a wide variety of speeds and directions. Preferably, initial flight parameters are measured over a short length of a ball's initial trajectory (e.g. not more than 5 meters but more preferably less than 2 meters) so that balls struck from adjacent tee-off bays do not interfere with the measurement. However, any means of measuring the initial launch parameters of one golf ball in the presence of other flying golf balls may be employed. The signal processing means requires data that identifies each tee-off bay in the driving range and records the range, azimuth direction and height of each tee-off spot relative to each target in the golf facility.
The time of impact of balls at the tee-off bays can be measured by sensing the impact sound using one or more microphones. If required, a crude measurement of ball launch speed and direction may be derived from analysis of signals from several microphones, possibly configured as a phased array. Alternatively, the time of impact can be measured by optical means, for example by detecting the passage of the ball through one or more optical detection planes. The said optical means may be configured to measure the time of impact and optionally at least one of ball launch speed, launch azimuth angle and launch elevation angle of each struck ball.